4.3 LX Low compression

[helimech2003]

Long story short. I traded for this boat over this last winter so I didn't really get a chance to look it over like I should have. The guy said it had a rebuilt engine in it and he thought it had less than 20hrs on it. No hour meter so???? Looking at the engine it does look like it has been pulled and gone through.
I decided to do a compression check on the engine due to the fact that it is having trouble turning what all the prop calculators say it should have.
Well, I did it cold to start with so I know the numbers will be low but they are all around 110 with the lowest being 95.
Do you guys think the numbers will come up as it breaks in or is it done???
It runs like a top and I do have a prop that it will turn so I can prob get through the summer and rebuild this winter.

 

[harleyman1975]

If you did not do it warm with throttle open you did not get accurate reading (low). if not using oil or producing blow by most likely you are ok. Run the prop that the engine likes and don't try to make that little 4.3 go FAST. just shoot for dependable.

 

[Rick Stephens]

What prop are you trying to run? And do you know what gear ratio the drive is?

 

[helimech2003]

What prop are you trying to run? And do you know what gear ratio the drive is?

14.25 x 19 4 blade. The ratio is 1.81.
Not looking to go fast. Getting to old for that. Just want something dependable

 

[Scott Danforth]

lets start at the beginning....... going back to the compression numbers.

did you dry a different gauge?

will all numbers being somewhat low, do a leak-down test to determine where the issue is (rings, valves, etc)

you may just need a valve adjustment, you may need a valve job, or someone did a half-fast (say it...) rebuild on the motor.

if you suspect rings based on the leak-down test, squirt a bit of oil in the cylinders to verify if its rings.

with a new rebuild motor, your compression numbers should be closer to 150psi

then we can go from there.

 

[Rick Stephens]

14.25 x 19 4 blade. The ratio is 1.81.
Not looking to go fast. Getting to old for that. Just want something dependable

That's about where I would start. I'm running a 21" 4 blade on a 17 footer.

Scott is right on the money on the motor.

 

[achris]

Can't put anything into cold engine compression numbers. Do the test with the engine warm and the throttle full open. Then post those here.